The present invention relates to tape feed devices for a sewing machine.
One such tape feed device is known from German Offenlegungsschrift No. 34 25 939 corresponding to U.S. Pat. No. 4,590,874. This device contains an electromechanical transducer, which is subjected to mechanical deformation by the force generated by the tape tension, which deformation is converted into an electrical signal. This signal is further processed and controls a drive roll to keep the tape tension constant. Although the tension adjuster is of a very complex design, there is the disadvantage that different tape tensions coming from the tape supply have a direct effect on the drive roll and hence a bad influence on the sewn product.
Another tape feed device is described in German Offenlegungsschrift No. 24 02 055. In this device, the speed of a drive roll is controlled by means of an arm, which is disposed between rolls, by way of a complex control device. This tape feed device also does not have any means for compensating for fluctuations in tape tension ahead of the drive roll.
It is particularly desirable to have a small and constant a tape tension as possible ahead of the drive roll is elastic tape with a defined tension is to be sewn into a workpiece, since fluctuations in tape tension can lead to changs in the length of the tape to be worked.